A lawyer for a B.C. First Nation is accusing the federal government of withholding key information about oil spills until after the latest consultation on the Trans Mountain pipeline was over.

Scott Smith, who represents the Tsleil-Waututh Nation, told the Federal Court of Appeal in Vancouver on Monday that the First Nation prepared three expert reports on the risks of oil spills and other environmental concerns surrounding the pipeline expansion.

A federal peer review of the reports effectively agreed with their findings that there is a lack of information about the effects and behaviour of diluted bitumen, but it wasn’t shared with the First Nation until after consultation closed, Smith said.

“Meaningful dialogue cannot occur where, as here, Canada withheld key documents until after the decision and refused to change its position even when its scientists agreed,” Smith said.

He also alleges the peer review was “substantially altered” before it was distributed with a note saying a report on diluted bitumen was not necessary to cabinet’s vote on the pipeline, effectively neutering the scientists’ conclusions.

The Tsleil-Waututh are among four B.C. Indigenous groups arguing in the court this week that the Canadian government came into the new round of consultations having predetermined the outcome before its latest approval of the Trans Mountain pipeline.

The Federal Court of Appeal tore up the government’s original approval of the pipeline in August 2018, citing inadequate Indigenous consultation among its reasons.

Lawyers for the Canadian government are expected to present arguments Tuesday.

Smith argued that Ottawa had already made up its mind about whether to approve the pipeline again before renewing the consultation. He pointed to public comments made by Prime Minister Justin Trudeau after the court quashed its initial approval, in which he said the project is in the “national interest,” as well as similar comments made by cabinet ministers.

“Canada simply refused to budge on any of these issues or change its position because it was unilaterally focused on reapproving the project and in the words of the minister of finance, ‘getting shovels into the ground,’ ” Smith said.

The result was another round of consultations that was “fundamentally flawed” before Ottawa’s latest approval of the pipeline expansion, he said.

Lawyers for the Coldwater Indian Band and a coalition of small First Nations in the Fraser Valley also presented arguments Monday.

Matthew Kirchner told the panel of three judges that the existing Trans Mountain pipeline cuts through the heart of the Coldwater reserve 12 kilometres southwest of Merritt in B.C.’s Interior.

The reserve relies entirely on the underlying aquifer for its drinking water and Ottawa has a fiduciary duty to protect it, he said.

“It is hard to conceive of an issue that is more fundamental, and of more fundamental importance to repairing Canada’s damaged relationship with Indigenous Peoples, than that of the protection of drinking water on reserve,” Kirchner told the court.

The band has requested a hydrogeological study since 2015, beginning with a two-year baseline report, in order to understand impacts on the aquifer.

Only two weeks before cabinet voted on the project, the Crown consultant emailed the First Nation’s chief on a Friday night providing him with vital information about how the aquifer would be analyzed and how a possible alternate route would be assessed, he said.

The chief was given until only the following Wednesday to provide a response, Kirchner said.

“There is no opportunity at all in there for meaningful dialogue,” he said.

The proposal set an arbitrary deadline for an aquifer assessment of Dec. 31, neglecting the two-year baseline review requested, he said.

The three-day hearing is scheduled to continue through Wednesday to consider legal challenges launched by the Tsleil-Waututh Nation, Squamish Nation, Coldwater Indian Band and a coalition of small First Nations in the Fraser Valley.

Several First Nations, environmental groups and the City of Vancouver had originally filed challenges making a range of arguments including that the project threatens southern resident killer whales.

The court only allowed six First Nations to proceed and called for an expedited hearing focused on the federal government’s consultation with Indigenous communities between August 2018 and June 2019.

Two First Nations have since dropped out of the appeal after signing deals with Trans Mountain Corp., the Crown corporation that operates the pipeline and is building the expansion.

The Tsleil-Waututh and environmental groups filed leave to appeal to the Supreme Court of Canada, arguing that a broader hearing was necessary, but the high court has not yet issued a decision.

Trudeau’s government has twice approved a plan to triple the capacity of the pipeline from Alberta’s oilsands to a shipping terminal in Metro Vancouver.

After the Federal Court of Appeal nixed the original approval, the Liberal government ordered the forerunner of the Canada Energy Regulator to conduct a new review focusing on marine impacts, which was completed in February.

The government also appointed retired Supreme Court justice Frank Iacobucci to oversee a new phase of consultation with affected Indigenous communities before it approved the project a second time in June.

The governments of Alberta and Saskatchewan, which support the pipeline expansion, have joined the case as interveners.